1. Field of the Invention
The present invention relates to reverberation effect adding devices which add reverberations to a musical sound.
2. Description of the Related Art
Generally, in reverberation effect adding devices, musical sound waveform data is subjected to a filtering process by a digital filter. As the digital filter, a FIR (Finite Impulse Response) filter or an FIR (Infinite Impulse Response) filter is used.
When the FIR filter is used, a convolution operation is performed between received musical sound signal data X[n−k] (k=0, 1, 2, . . . , n−1) and an impulse response a[k] obtained from a reverberation characteristic of a music hall, thereby providing resonance data Y[n]=Σx[n−] ×a[k].
For example Japanese Published Unexamined Patent Application 2007-202020 discloses a first signal processing system which convolutes a direct sound part of an impulse response and a second signal processing system provided in parallel with the first signal processing system and which convolutes a reflected sound part of an impulse response such that the second signal processing system uses a downsampled sampling signal compared to the first signal processing system.
This techniques requires not only a convolution operation circuit which includes the two FIR filters, but also two system impulse response data. Thus, many circuit components and data are required. Since the two signal processing systems are provided in parallel, the impulse response coefficients can be zero such that one of the signal processing systems does not virtually perform the operation and hence parts of the circuits and operations becomes useless.
It is therefore an object of the present invention to provide a reverberation effect adding device which includes no useless circuits and which is capable of producing a high quality reverberation continuing for a long time.